JPH08137360A - Image forming device - Google Patents

Abstract

PURPOSE: To widen the detecting area of an image position measuring pattern in a constant memory space. CONSTITUTION: Main- and sub-sampling densities are set in main- and sub- scanning memories A and B storing images read by sensors A and B and then, writing start and completion positions are set in comparators by a CPU respectively. The set values of each memory and the counter values of main- and sub-scanning counters are compared with the comparators to set the writing valid ranges of the memories. After writing data in the memories with the sampling densities specified by main- and sub-scanning memory sampling density setting means, the CPU calculates a positional deviation in an image based on data in the memories. The reading range of the next image is set from the result. The calculation is executed in the block of each color, finally the positions of the images in several blocks are calculated and the averaged result for each color is used for controlling the positional deviation in an image forming device. Thus, a pattern detecting area is widened with a constant memory capacity and a large positional deviation in the image can be detected as well.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus such as a laser beam copying machine and a printer, and more particularly to a multiple image forming apparatus having a plurality of image forming apparatuses, and more particularly to correcting a shift of a transfer image forming position. The present invention relates to a registration correction device capable of obtaining good image quality.

[0002]

2. Description of the Related Art When sequentially transferring images formed by a plurality of image forming units onto a recording medium, if the transfer image forming position is displaced from the ideal position for each image forming unit, the tint will be different or the color shift will occur. The resulting image is uneven and good image quality cannot be obtained. Therefore, for example, by using the image position detection sensor, the image position measurement pattern on the transfer / conveying belt formed by each image forming apparatus is read, and the amount of deviation of each color is calculated by the image position detection processing circuit. A method has been proposed in which a good amount of color misregistration is obtained by correcting the amount in each image forming apparatus. FIG. 4 shows an example of the image position measurement pattern, and the image position interval is determined so that position fluctuations, speed fluctuations, and CCD vibrations of the transfer belt can be eliminated as much as possible. FIG. 5 is a diagram showing a conventional pattern detection area in the main scanning direction and the sub scanning direction. X ₁ and X ₂ are pattern detection widths in the main scanning direction, and Y ₁ and Y ₂ are pattern detection widths in the sub scanning direction. Show. The pattern detection area is X × Y, and is limited by memory restrictions and calculation time. When reading the main scanning image position measurement pattern, for example, the sub-scanning direction pattern detection width is fixed at 16 lines, and the sensor resolution is 14
When processing is performed with a um, 32 Kbit memory and a resolution of 8 Bit, the pattern detection width in the main scanning direction is only about 3.6 mm, which corresponds to 256 dots, and the allowable range for the variation of the transfer image forming position is ± 1.8 mm.

[0003]

However, in the above-mentioned apparatus, the image position measurement pattern must be detected within a limited area, and the difference in the mounting error of the image forming apparatus, the speed fluctuation of the transfer belt, etc. Therefore, it may happen that the image cannot be detected at the predicted position. To prevent this, a wide pattern detection area can be solved, but a large amount of memory is required and the cost of the entire apparatus increases. In addition, since the amount of data is large, it takes a long time to calculate the image position, which causes a problem that the image cannot be processed until the image is taken into the memory next time. An object of the present invention is to provide an image forming apparatus capable of expanding the detection area of an image position measurement pattern in a fixed memory space.

[0004]

In order to achieve the above object, the image forming apparatus according to the invention of claim 1 detects an image position measuring pattern transferred from a plurality of image forming units onto a conveyor belt. A detection unit, an image memory for storing the image position measurement pattern image output from the image position detection unit, and a main scanning of the sampling density to the image memory,
Density setting means that can be arbitrarily set for both sub-scanning, writing position setting means that sets a writing start position and ending position in the image memory, and computing means that calculates the deviation of the image position from the data in the image memory The control means controls the density setting means and the writing position setting means based on the result from the computing means. According to a second aspect of the invention, in the first aspect of the invention, the sampling density set by the density setting means is usually low, and the sampling density after pattern detection is high. Image forming device. Preferably, the following sampling modes are possible. At the time of reading the scanning image position measuring pattern, sampling is performed at a low density in at least the main scanning direction. At the time of reading the sub-scanning image position measuring pattern, sampling is performed at least in the main scanning direction with low density. After patterning a pattern composed of images of a plurality of colors at low density, the next pattern is sampled at high density. Only the first image of the pattern consisting of images of multiple colors is sampled at low density, and then the next image is sampled at high density. When reading the pattern for measuring the main scanning image position, sampling is performed at a low density, and after image detection, sampling is performed at a high density within the same image. Prior to reading the sub-scanning image position measuring image, the main scanning image position measuring image is read. The main-scanning position measurement image is sampled at a low density before the sub-scanning position measurement image, and after the image detection, the sub-scanning position measurement image is read. The main scanning position measuring image is a pattern arranged above the sub scanning position measuring image.

[0005]

According to the first aspect of the invention, the image position measuring pattern transferred from the plurality of image forming units onto the conveyor belt is detected and stored in the image memory. When the image of this measurement pattern is stored in the image memory, the sampling density for the image memory is set to main scanning and sub scanning, and the writing start position and end position for writing to the image memory are set. The shift of the image position is calculated by. By performing the density setting and the writing position setting based on the result, the pattern detection area can be widened with a constant memory capacity, and a large image position shift can also be detected. According to the structure of claim 2, the pattern is detected at a low density,
By performing high-density reading after the image position shift calculation, accurate correction can be realized without losing sight of the image position measurement pattern.

[0006]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows a schematic structure of an image forming apparatus according to the present invention.
This is simply an example of application to an image forming apparatus). FIG. 2 is a schematic diagram of a color misregistration correction system in a multi-transfer type color image forming apparatus. In FIG. 1, a document 2 set on a platen glass 1 is scanned by a document scanning device, and a read document image is input to a CCD sensor 3 through a lens 16 and converted into a color image signal to an image processing device 4. send. The image processing device 4 edits the color image signal,
An image signal is sent to each of the Y, M, C and K devices.

Each of the Y, M, C and K devices is a writing device 5,
It comprises a photoconductor 6 and a developing device 7. Any of the above devices may be used as long as it is a combination of a photoconductor and a laser beam ROS or LED ROS. Here, Y is a device that forms a yellow image, M is a device that forms a magenta image, C is a device that forms a Sian image, and K
Is a device for forming a black image, and these YMCK devices are arranged at substantially equal intervals.

The transfer member 8 has a transparent belt structure for transferring an image formed by each of Y, M, C and K devices, and is supported by a driving roller 9 and a driven roller 10 which face each other. The driving roller 9 is driven by a dedicated driving motor (not shown) having excellent constant speed, and the driven roller 10 is rotated by its driving force being transmitted by the transfer belt 8. The transfer belt 8 also has a function of carrying the transfer paper 11. The transfer paper 11 is fed from the paper tray 12, is temporarily stopped by the registration roll 13, and is transferred onto the transfer belt 8 in synchronism with the timing of the image forming process.
Transported from right to left. At this time, a suction corotron (not shown) is provided to suck the paper 11 onto the belt member.

A transfer corotron (not shown) is arranged so as to face the photoconductor 6 of each apparatus via the transfer belt 8, and each transfer corotron is controlled according to the image forming process of each color. The color toner images formed on the photoconductor are sequentially transferred to a transfer paper. The sheet after transfer is fixed by the fixing device 14 and discharged to the discharge tray 15. In the present embodiment, as shown in FIG. 2, a CCD as an image detecting means for reading the image recorded on the transfer belt 8 formed by the Y, M, C, and K devices on the downstream side of the K device is used. Two image pickup elements 101 such as 1 are arranged at both ends of the image area, that is, two in total.

CCD 1 mounted on the assay body 103
01 and its drive circuit and optical system, for example, the mounting positional relationship of the SELFOC lens or the like is designed so that highly accurate positioning can be easily realized. Light source 102 is CCD 101
Generates background light necessary for detecting an image on the transfer belt 8, and an LED, a halogen lamp or the like is used. Any light source can be used as the light source of the CCD 101 as long as it can secure a sufficient amount of light. In addition, the light source 102 deteriorates the light amount of the light source itself, the transmittance of the transfer belt 8, and the CCD 101.
In order to secure an optimum image receiving state, the amount of light can be freely changed with respect to sensitivity deterioration, deterioration of transmittance due to dirt on the optical system, and environmental changes represented by temperature.

Next, the normal image forming mode will be described. When the leading edge of the sheet conveyed by the transfer belt 8 reaches the transfer point directly below the Y apparatus, the leading edge of the image formed by the Y apparatus reaches the transfer point directly below the Y apparatus, that is, the image and the sheet. The paper feed timing and the image writing timing are determined so that there is no deviation in the sub-scanning direction (paper transport direction) between them. On the sheet that has reached the transfer point, the image formed by the Y device is transferred by a transfer corotron (not shown), and further reaches the transfer point directly below the M device. The sheet that has reached the transfer point directly below the M apparatus is transferred in the same manner as it was transferred by the K apparatus, and is transferred over the image transferred by the Y apparatus.
Hereinafter, similar overwriting is performed in the C and K devices.

The sheet on which all the transfer has been completed is further conveyed by the transfer belt, and when it reaches the vicinity of the driving roll 10,
The sheet is separated from the transfer belt by a corotron, a stripper, or the like (not shown) for separating the sheet from the transfer belt. After that, it is fixed by the fixing device 14 and the like, and is discharged to the outside of the machine.

In FIG. 2, the interface board 10
Reference numeral 4 includes a Y interface board, an M interface board, a C interface board, and a K interface board, and sends an image signal to the ROS 105 of each device. The registration misregistration correction board 106 is different from the interface board 104 in that side registration correction and lead
The registration / misregistration correction system for instructing registration correction and the memory / image processing board 109 collectively manage the memory and the image processing relationship. The control board 107 controls the operation of the boards 106 and 109 and the entire apparatus.

Next, the operation of the registration shift correction system will be described. The registration shift correction is performed by entering a dedicated correction cycle preset in the apparatus. In the correction cycle, the control board 107 issues a command to each board, and the interface board 104 plays the role of a pattern generator that outputs a pattern for measuring registration deviation. Further, the registration deviation correction board 106 receives a signal from the interface board 104, and prepares to sample a registration deviation measurement pattern output from each device.

When the correction cycle starts, first, the registration deviation measuring pattern output from the interface board Y by the Y device is transferred onto the transfer belt 8 as a record 108Y. After the registration deviation measurement pattern is transmitted from the interface board Y to the Y apparatus, the registration deviation measurement pattern is continuously transmitted from the interface board M to the M apparatus with a time difference according to the distance between the transfer points of the Y apparatus and the M apparatus. Will be sent. The registration deviation measurement pattern formed by the M apparatus is transferred onto the transfer belt 8 as shown by a record 108M. At this time, the pattern of the recording 108M is a pattern in which a registration deviation measuring pattern is further overwritten on the recording 108Y which has already been transferred. Similarly, the recordings 108C and 108K by the C device and the K device are
It is overwritten as a pattern for measuring the registration shift. The completed recording of the pattern for measuring the registration shift is made in advance by the transfer belt 8 so as to reach directly below the CCD 101.

The registration deviation correction board 106 monitors at least one of the pattern output timings for measuring the registration deviation of the interface board 104 by sampling the image data from the CCD 101. From the output timing of at least one interface board, the time when the pattern for measuring the registration shift reaches just below the CCD 101 is determined. That is, the sampling start timing and the sampling end which are necessary and sufficient for sampling the registration deviation measurement pattern from the pitch and the driving frequency between the device for forming the registration deviation measurement pattern output from the interface board and the CCD. You can figure out the timing.

At the sample start timing, the registration shift correction substrate 106 starts to capture the image signal from the CCD 101 into the high speed memory, and at the sample end timing, the capture is finished. At the same time as the end of capturing, before the sample of the pattern for measuring the next registration deviation is completed,
The image position is determined from the captured data by, for example, the barycentric method, and is stored in the main memory as an image position address, for example. By repeating this operation several times, several fixed image position addresses can be obtained for each device. Here, in order to improve the accuracy of the fixed image position address, these several fixed image position addresses are
An average may be taken for each device.

Next, a correction value for correcting the registration deviation between the respective devices is calculated by a predetermined algorithm from the image position address determined for each device for each registration deviation correction parameter and for each device. Calculate to. By setting the calculated correction values from the registration deviation correction board to each device, each interface board, and the like, it is possible to provide image quality without registration deviation. The misregistration has various misalignment patterns due to the process direction, the lateral direction, the magnification, and the skew, and is usually caused by a combination of these. Various misalignments are read with the measurement pattern and the pattern is measured. Then, correction is made according to the measured pattern.

FIG. 3 shows a control block of the registration correcting apparatus showing an embodiment of the present invention. CCD 10
The analog signals of the images read by the sensors A and B configured by 1 have high-frequency components removed by a filter circuit (not shown), amplified by an amplifier, and offset-adjusted, and then converted to, for example, 8 bits by an A / D converter. Is quantized. First, the main scanning memories A and B and the sub-scanning memories A and B have CPUs.
After setting the main and sub-sampling densities, the write start position and end position are set in the comparator by the CPU, respectively, and the write start and end set values for the main scanning memories A and B and the sub-scanning memories A and B and the main scanning are set. The counter values of the counter and the sub-scanning counter are compared by the main comparator and the sub-comparator, respectively, and the write effective range of the memory is set. When each is set, it is written in the memory at the sampling density specified by the main scanning memory sampling density setting means and the sub-scanning memory sampling density setting means.

When the writing in the memory is completed, the data in the memory is transferred to the CPU, the image position is calculated by the CPU, and the reading range of the next image is set based on the result. If there is no time to perform the image position shift calculation processing and the setting of the reading range of the next image due to the narrow space between the patterns, the data in the memory is transferred to the CPU and then the reading range of the next image is set and written in the memory. After preparation, the CPU performs image position shift calculation. In this way, the calculation for each color is performed in the block, and finally the result of averaging the image position calculation results of several blocks is used for the positional deviation control of the image forming apparatus. Although there are main and sub comparators for the sensors A and B in FIG. 3, one main scanning and one sub scanning may be provided.

(First Embodiment) FIG. 6 is an explanatory view in the case of correction in the main scanning direction. After the image position measurement pattern is written, the CPU first sets the sampling density in the main scanning direction, and sets the main scanning image position measurement pattern detection start address and the end address according to the sampling density. In the setting of the sub-scanning direction, the purpose is to measure the amount of deviation of the image position in the main scanning direction in this case, so there is no need to make the sampling density particularly coarse, and the width of the detection area is also the image in the main scanning direction. Only a sufficient number is required to average the position data in the sub-scanning direction. For example, 8 lines or 16
If it is set to 2 ⁿ (n = 1, 2, 3, 4, ...) For the line, the division for averaging can be performed by bit shift. It can be executed at a low cost with a simple configuration, and in a short period of time when implemented by software.

In FIG. 6, (a) shows a pattern detection area in which the sampling density is not changed. This example is shown in (b) and (c). That is, (b) shows the pattern detection area in which the main scanning sampling density is halved and the sub scanning is fixed. (C) is a diagram showing a pattern detection area when the sampling density is set to 1/2 in both main scanning and sub scanning. The setting of the sampling density is arbitrary. First
According to the embodiment described above, the pattern detection area can be expanded with a constant memory capacity by making the sampling density variable. When the sampling density is lowered, the resolution deteriorates, but when the image position is calculated by the centroid method or the like, almost no error occurs.

An example is shown in FIG. In the case of image position data having a bilaterally symmetrical distribution as shown in FIG. 13A, the results of normal sampling density and 1/2 low sampling density are exactly the same, and the address of the center of gravity of the image position is determined by the center of gravity method. Then, the center of gravity becomes the position of address 5. FIG.
In the case of image position data having an asymmetric distribution as shown in (b), when the address of the center of gravity of the image position is calculated up to 3 digits after the decimal point by the center of gravity method, the center of gravity address at normal sampling density is obtained. 5.273, and the center-of-gravity address at a low sampling density of 1/2 is 5.214. The difference is 0.059, which is 0.8261 um and an error of 1 um or less when a sensor having a 14 um pixel size is used.

(Second Embodiment) FIG. 7 shows an explanatory diagram in the case of correction in the sub-scanning direction. It can be considered as in the case of correction in the main scanning direction. (A) shows a pattern detection area in which the sampling density is not changed. (B) shows a pattern detection area in which the sub-scanning sampling density is halved and the main scanning is fixed. FIG. 6C is a diagram showing a pattern detection area when main scanning and sub-scanning and the sampling density are halved. The setting of the sampling density is arbitrary.
According to this embodiment, it is effective in improving the mechanical accuracy that varies in the sub-scanning direction.

(Third Embodiment) FIG. 8 shows the patterns and detection areas of the first two blocks in a continuous block. In the detection of the image for measuring the main scanning position of the first block, each color is sampled with a low density in the main scanning direction and a high density in the sub scanning direction, and in the case of the sub scanning position measurement, a low density in the sub scanning direction, The main scanning direction is stored in the memory with a high density, and the detection area is widened in the necessary direction to calculate the image position deviation. The figure shows the latter. At the time of image detection of the next block, the pattern detection start address and end address are set to optimum positions for each color based on the image position information for each color calculated in the first block, and high density sampling is performed. According to the third embodiment, accurate correction can be performed without losing sight of the pattern, and coarse adjustment,
Since it is not necessary to perform the correction cycle in two steps, that is, the fine adjustment, the correction time can be greatly shortened. FIG. 14 shows a schematic flowchart.

The image position measurement pattern is written (S1), the sampling density in the main scanning direction is set to a low density (S2), and the memory write start and end addresses are set (S3). When the image acquisition to the memory is completed (S4), the contents of the memory are transferred to the CPU (S5), and C
The image position is calculated by the PU (S6). The result is stored in each color register (S7). After performing the above processing for all four colors (S8), set high-density sampling (S8).
9), memory write start and end addresses are set (S10). Then, the image is taken into the memory (S
11) At the end of the process, the contents of the memory are transferred to the CPU (S12). The CPU calculates the image position shift amount,
The result is averaged with the previous result of the same color and stored in the register (S14). After performing the operation for four colors (S15),
A predetermined number of times for averaging this is performed based on the result of several blocks (S16), and the process is ended.

(Fourth Embodiment) FIG. 9 shows a method of roughening the sampling density at the time of the first pattern detection and reflecting the result in the detection areas of the respective colors in the same block for batch processing. Is. This embodiment is effective when the pattern interval is wide.

(Fifth Embodiment) FIG. 10 shows that when the main scanning image position measurement pattern is detected, the sampling density is made coarse in both the main scanning direction and the sub scanning direction, and the pattern detection area is narrowed immediately after the pattern detection. Then, a method for performing accurate correction within the same pattern is shown.

(Sixth Embodiment) FIG. 11 shows a pattern in which the image of the main scanning position measurement can be detected prior to the sub scanning position measurement, and the sampling is first performed at a low density in both the main scanning direction and the sub scanning direction. The method for setting the sub-scanning position measurement detection area immediately after detecting the main-scanning position measurement image is shown. According to the present embodiment, the memory is used, but since the data can be sequentially processed in the main scanning direction without using the memory, the detection area can be expanded by the width of the reading area of the sensor in the main scanning direction. it can.

(Seventh Embodiment) FIG. 12 shows a pattern which enables the main scanning position measurement image to be detected before the sub-scanning position measurement image, as in the sixth embodiment. According to the present embodiment, the effective width of illumination can be shortened by placing the main scanning image above the sub scanning image.

[0031]

As described above, according to the first aspect of the invention, the pattern detection area can be widened with a constant memory capacity by varying the sampling density when reading the image position measurement pattern into the memory. Therefore, it is possible to detect a large image position deviation, and it is possible to widen the tolerance range for the error of the belt drive system, the mounting accuracy of the image forming unit, and the variation. Further, by detecting the pattern at a low density, calculating the image position shift, and then reading at a high density, it is possible to realize accurate correction without losing sight of the image position measurement pattern. In addition, the sub-scanning position measurement image, which is difficult to detect the pattern due to the mounting accuracy of the image forming apparatus, the transfer belt speed error, etc., is detected, and then the sub-scanning position image is measured based on the result. By setting the pattern detection area for the image, it is possible to easily detect the pattern and it is possible to realize an inexpensive and highly accurate image forming apparatus.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of an image forming apparatus according to the present invention.

FIG. 2 is a schematic diagram of a color misregistration correction system in a multi-transfer type color image forming apparatus.

FIG. 3 is a control block diagram of a registration correction device.

FIG. 4 is an explanatory diagram showing an example of an image position measurement pattern.

FIG. 5 is an explanatory diagram of a conventional pattern detection area in a main scanning direction and a sub scanning direction.

FIG. 6 is an explanatory diagram of the first embodiment.

FIG. 7 is an explanatory diagram of the second embodiment.

FIG. 8 is an explanatory diagram of the third embodiment.

FIG. 9 is an explanatory diagram of the fourth embodiment.

FIG. 10 is an explanatory diagram of the fifth embodiment.

FIG. 11 is an explanatory diagram of the sixth embodiment.

FIG. 12 is an explanatory diagram of the seventh embodiment.

FIG. 13 is a diagram showing an example of calculating the image position by the center of gravity method when the sampling density is changed.

FIG. 14 is a diagram showing a schematic flowchart for detecting an image position shift.

[Explanation of symbols]

1 ... Platen glass, 2 ... Original, 3 ... CCD sensor, 4
... image processing device, 5 ... YMCK device, 6 ... photoconductor, 7 ...
Developing device, 8 ... Transfer belt, 12 ... Paper tray, 14 ... Fixing device, 101 ... CCD sensor, 102 ... Light source, 104
... interface board, 106 ... registration correction board, 10
7 ... control board, 108 ... measurement pattern, 10
9 ... Memory / image processing board

Claims (2)

[Claims] 1. An image position detecting means for detecting an image position measuring pattern transferred from a plurality of image forming portions onto a conveyor belt, and an image memory for storing image position measuring pattern images output from the image position detecting means. A density setting means capable of arbitrarily setting a sampling density to the image memory for both main scanning and sub-scanning; a writing position setting means for setting a writing start position and an ending position to the image memory; An image forming apparatus comprising: a calculation unit that calculates the deviation of the image position from the data of 1 .; and a control unit that controls the density setting unit and the writing position setting unit based on the result from the calculation unit. 2. The image forming apparatus according to claim 1, wherein the sampling density set by the density setting means is normally low and the density after pattern detection is high.